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Author

Yim-Shu Lee

Other affiliations: Ericsson
Bio: Yim-Shu Lee is an academic researcher from Hong Kong Polytechnic University. The author has contributed to research in topics: Converters & Power factor. The author has an hindex of 27, co-authored 104 publications receiving 2988 citations. Previous affiliations of Yim-Shu Lee include Ericsson.


Papers
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Journal ArticleDOI
TL;DR: A converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated, which has very good current sharing characteristics even in the presence of relatively large duty cycle mismatch.
Abstract: Boost converters are widely used as power-factor corrected preregulators In high-power applications, interleaved operation of two or more boost converters has been proposed to increase the output power and to reduce the output ripple A major design criterion then is to ensure equal current sharing among the parallel converters In this paper, a converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated The boost converter cells have very good current sharing characteristics even in the presence of relatively large duty cycle mismatch In addition, it can be designed to have small input current ripple and zero boost-rectifier reverse-recovery loss The operating principle, steady-state analysis, and comparison with the conventional boost converter are presented Simulation and experimental results are also given

570 citations

Journal ArticleDOI
TL;DR: The proposed fuzzy control scheme is evaluated by computer simulations as well as experimental measurements of the closed-loop performance of simple DC/DC power converters in respect of load regulation and line regulation.
Abstract: The design of a fuzzy logic controller for DC/DC power converters is described in this paper. A brief review of fuzzy logic and its application to control is first given. Then, the derivation of a fuzzy control algorithm for regulating DC/DC power converters is described in detail. The proposed fuzzy control scheme is evaluated by computer simulations as well as experimental measurements of the closed-loop performance of simple DC/DC power converters in respect of load regulation and line regulation.

272 citations

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TL;DR: In this paper, a model of a parallel multi-inverter system with instantaneous average current sharing is presented, where a disturbance source is introduced to represent all the sources that may cause current unbalances.
Abstract: Parallel multi-inverter systems can be designed to have the advantages of expandable output power, improved reliability, and easy N+X redundancy operation. However, a current-sharing control scheme has to be employed to enable the inverters to share the load current equally. A multi-inverter system with instantaneous average-current-sharing scheme is presented in this paper. By introducing a disturbance source to represent all the sources that may cause current unbalances, a model of the system can be built. Some key issues are discussed based on the model, including stability of the current-sharing controller, impedance characteristics and voltage regulation. Three experimental 110 VAC/1.1 kVA inverters are built and paralleled to verify the theoretical predictions.

257 citations

Journal ArticleDOI
TL;DR: An actively clamped bidirectional flyback converter is proposed and it is found that the flow of current is directly under the control of the duty cycle, and that the transformer's leakage inductance has a significant effect on the control characteristic of the converter.
Abstract: An actively clamped bidirectional flyback converter is proposed. The converter's operation is examined in detail. All switches in the converter have zero-voltage-switching characteristics. A low-frequency behavior model and small-signal transfer functions are derived. It is found that the flow of current is directly under the control of the duty cycle, and that the transformer's leakage inductance has a significant effect on the control characteristic of the converter. It is expected that such bidirectional converters will find wide applications in the interconnection of multiple sources of DC power to a common bus (e.g., in a DC uninterruptible power supply). Simulation and experiment results are also presented.

169 citations

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TL;DR: This paper presents a neural network with a novel neuron model that has two activation functions and exhibits a node-to-node relationship in the hidden layer, and provides better performance than a traditional feedforward neural network, and fewer hidden nodes are needed.
Abstract: This paper presents a neural network with a novel neuron model. In this model, the neuron has two activation functions and exhibits a node-to-node relationship in the hidden layer. This neural network provides better performance than a traditional feedforward neural network, and fewer hidden nodes are needed. The parameters of the proposed neural network are tuned by a genetic algorithm with arithmetic crossover and nonuniform mutation. Some applications are given to show the merits of the proposed neural network.

116 citations


Cited by
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Journal ArticleDOI
01 Nov 2009
TL;DR: The hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to MGs is presented and results are provided to show the feasibility of the proposed approach.
Abstract: DC and AC Microgrids are key elements to integrate renewable and distributed energy resources as well as distributed energy storage systems. In the last years, efforts toward the standardization of these Microgrids have been made. In this sense, this paper present the hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to microgrids. The hierarchical control proposed consist of three levels: i) the primary control is based on the droop method, including an output impedance virtual loop; ii) the secondary control allows restoring the deviations produced by the primary control; and iii) the tertiary control manage the power flow between the microgrid and the external electrical distribution system. Results from a hierarchical-controlled microgrid are provided to show the feasibility of the proposed approach.

4,145 citations

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TL;DR: This paper presents an exhaustive review of three-phase improved power quality AC-DC converters configurations, control strategies, selection of components, comparative factors, recent trends, their suitability, and selection for specific applications.
Abstract: Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

1,691 citations

Journal ArticleDOI
TL;DR: A survey on recent developments (or state of the art) of analysis and design of model based fuzzy control systems based on the so-called Takagi-Sugeno fuzzy models or fuzzy dynamic models.
Abstract: Fuzzy logic control was originally introduced and developed as a model free control design approach. However, it unfortunately suffers from criticism of lacking of systematic stability analysis and controller design though it has a great success in industry applications. In the past ten years or so, prevailing research efforts on fuzzy logic control have been devoted to model-based fuzzy control systems that guarantee not only stability but also performance of closed-loop fuzzy control systems. This paper presents a survey on recent developments (or state of the art) of analysis and design of model based fuzzy control systems. Attention will be focused on stability analysis and controller design based on the so-called Takagi-Sugeno fuzzy models or fuzzy dynamic models. Perspectives of model based fuzzy control in future are also discussed

1,575 citations

Journal ArticleDOI
TL;DR: This paper reviews the status of hierarchical control strategies applied to microgrids and discusses the future trends.
Abstract: Advanced control strategies are vital components for realization of microgrids. This paper reviews the status of hierarchical control strategies applied to microgrids and discusses the future trends. This hierarchical control structure consists of primary, secondary, and tertiary levels, and is a versatile tool in managing stationary and dynamic performance of microgrids while incorporating economical aspects. Various control approaches are compared and their respective advantages are highlighted. In addition, the coordination among different control hierarchies is discussed.

1,234 citations

Journal ArticleDOI
TL;DR: In this paper, the authors comprehensively review and classify various step-up dc-dc converters based on their characteristics and voltage-boosting techniques, and discuss the advantages and disadvantages of these voltage boosting techniques and associated converters.
Abstract: DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

1,230 citations